This invention relates to a process for cleansing waste halides from a waste gas stream containing waste halide impurities.
The commercial production of metallic or nonmetallic halides (such as TiCl.sub.4) often results in a waste gas which contains small amounts of waste halides in a gaseous state. The waste gas can be predominantly a purge gas, such as nitrogen, or it can be a mixture of other gases, such as CO, CO.sub.2, N.sub.2, halogen, and acid halide. Disposal of the waste gas by venting directly to the atmosphere, even after conventional scrubbing (water-dilute acid scrubbing), results in an optically dense cloud caused by hydrolysis of the small amount of waste halides present. Thus, it is aesthetically desirable to have essentially complete removal of the small amount of waste halides prior to venting the waste gas into the atmosphere.
This problem has been recognized and various techniques have been tried to eliminate plume formation in waste gas streams. One such approach is disclosed in U.S. Pat. No. 3,460,900, to Moldovan et al., which relates to a process for removing titanium tetrachloride from the gases resulting from furnaces used in the chlorination of titaniferous materials by contacting the gases with aqueous solutions of 20-33% HCl or 20-98% H.sub.2 SO.sub.4 at temperatures of 5.degree.-50.degree. C. A disadvantage of Moldovan's process is that a gaseous stream containing TiCl.sub.4 is passed through an acid solution in an undispersed phase. This is expensive and inefficient since it requires large amounts of acid. Thus, there is a need for a process which efficiently removes all waste halide impurities from a gas stream.
U.S. Pat. No. 3,564,817, to Kleinfelder et al., relates to a process for removing small amounts of titanium tetrachloride and other chloride impurities from waste gas produced during chlorination of a titaniferous ore by first acid scrubbing the gas with sulfuric acid of 75-95 weight percent concentration, scrubbing the separated gas with water, and then venting the gas from the water scrubbing apparatus to the atmosphere. A disadvantage of this process is that once the TiCl.sub.4 is absorbed into the sulfuric acid titanyl sulfate forms and consumes some of the acid. Further, the remaining sulfuric acid present in solution with the titanyl sulfate cannot be recovered and reused in the process because the acid cannot be distilled out of the solution. Instead, the remaining acid must be neutralized and disposed of. Thus, there is a need for a process for removing waste halides from a waste gas stream using an aqueous acid which is not consumed when contacted with the waste halide and which can be recovered and reused in the process.